The present invention relates to a high-voltage edge termination for planar structures formed of a semiconductor body of one conductivity type whose edge area is provided with at least one field plate isolated from the latter by an insulator layer.
For decades now, efforts have been made to configure the field-strength profile obtained in the semiconductor body in the case of semiconductor components, such as diodes, such that breakdown does not take place in the edge area but rather in the main structure orxe2x80x94in the case of integrated configurationsxe2x80x94in the cell array. This is because the curves in the electric field which are inevitably present at the edge structure make the latter particularly susceptible to breakdown, so that moving the breakdown region into the main structure or the cell array simultaneously increases the breakdown strength of the semiconductor component.
A long-standing procedure for increasing the breakdown strength of the edge area of semiconductor components is provided by the use of field plates. Other measures for increasing the dielectric strength of edge structures in semiconductor components relate to the use of guard rings, which may possibly be connected to the field plates, the avoidance of pn-junctions with a large curvature in order to prevent field-strength peaks, etc. (see also Published, European Patent Application EP 0,037,115 A, for example).
Although intensive work has thus been carried out for a long time to increase the breakdown strength of the edge area of semiconductor components, there are still no entirely satisfactory results to date. It is still being contemplated how the breakdown strength of edge structures in semiconductor components can be easily increased.
Thus, the present invention is based on the object of creating a high-voltage edge termination structure for planar structures, which can be used to improve further the breakdown strength of semiconductor components in their edge area.
It is accordingly an object of the invention to provide a high-voltage edge termination for planar structures which overcomes the above-mentioned disadvantages of the prior art devices of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a high-voltage edge termination structure for planar structures, including:
a semiconductor body having an edge area and formed of a first conductivity type;
an insulator layer disposed on the semiconductor body;
at least one field plate isolated from the semiconductor body by the insulator layer; and
floating regions of a second conductivity type disposed in the edge area of the semiconductor body, the floating regions spaced at such a distance from one another that zones between the floating regions being depleted even at an applied voltage which is low in comparison with a breakdown voltage of the semiconductor body for the floating regions.
The invention achieves this object with a high-voltage edge termination for planar structures of the type mentioned in the introduction in that the edge area of the semiconductor body with the floating (or zero-potential) regions of the second conductivity type which are spaced to be at such a distance from one another that the zones between the floating regions are depleted even at an applied voltage which is low in comparison with the breakdown voltage of the semiconductor body for the floating regions.
When a voltage is applied, the floating regions, which can be provided in the manner of islands or else cohesively in a wedge shape with a narrowing thickness toward the edge on a plurality of essentially mutually parallel levels, act as though the edge area itself was undoped. The result of this is that, for the first time, the breakdown now takes place not in the edge area but rather in the center of a semiconductor component.
When insular regions of the second conductivity type are used, they may have essentially the same shape, for example spherical or elliptical. Similarly, it is also possible for the floating regions to have different shapes.
The floating regions also do not need to be completely depleted when a voltage is applied. This particularly applies to voltages that are significantly below the breakdown voltage in the central area of the semiconductor component.
The insular floating regions can also be of a cohesive configuration if appropriate. They are then in the form of a network or lattice. Furthermore, the insular regions can also extend into the central area of the semiconductor body of the semiconductor component.
Instead of configuring the floating regions to be wedge-shaped, they can also be provided with the same layer thickness and, for this, the surface doping can be decreased from, for example, 1012 cmxe2x88x922 down to 0 toward the edge. Such weaker doping toward the edge can also be provided for insular floating regions. In the same way, it is also possible to have the number of floating regions decrease toward the edge with the same doping or else progressively weaker doping. Hence, it is essential that the doping quantity introduced by the floating regions decreases toward the edge of the semiconductor component.
If appropriate, it is also possible to provide an injector or a Schottky contact which is capable of weakly injecting charge carriers of the second conductivity type in order thereby to prevent complete suppression of the current path when the space-charge zones are empty in the turned-on state.
The field plate provided in the insulator layer can be configured such that its distance from the semiconductor body becomes greater gradually or continuously as the edge of the semiconductor component is approached. It is also possible to provide stepped field plates made of a plurality of materials and, if appropriate, to connect them using guard rings. If one conductivity type is the n-conductivity type, then the guard rings are formed by p-conductive guard rings.
If the floating regions are on a plurality of essentially mutually parallel levels, then, when a voltage is applied to the semiconductor component between the anode and the cathode, for example, the space-charge zone in the semiconductor area between the cathodic surface of the semiconductor body and the first level of the floating regions is depleted first, in the case of an n-conductive semiconductor body. If the space-charge zone reaches the floating regions, then the potential remains at the value Vpth adopted at that time. Subsequently, the space-charge zone between the first level of floating regions and the second level develops. If the second level is reached by the space-charge zone, then the potential remains at a value of about 2 Vpth, so long as the individual levels are at essentially the same distance from one another.
In this manner, the whole edge area is successively depleted, so that the breakdown voltage can be increased to approximately N+1 times the normal value determined by the doping, assuming that N represents the number of levels.
If there is an injector, this serves, in an n-conductive semiconductor body, as a hole supplier for discharging the p-conductive floating regions in the turned-on state.
Suitable dimensions for the floating regions, if they are of insular construction, are a diameter of about 5 xcexcm for the spherical floating regions, with a mutual distance apart also of about 5 xcexcm, and the surface doping in the floating regions can be about 1012 to 1013 cmxe2x88x922.
The edge termination according to the invention can advantageously be used, by way of example, in super high-voltage insulated gate bipolar transistor (IGBT) or high-voltage field-effect transistors etc.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a high-voltage edge termination for planar structures, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.